booth



Feb. 7', 1956 s. w. BOOTH 2,733,659

DELAYED ARMING FUZE FOR A PROJECTILE Filed Aug. 5, 1949 meets-Sheet lFIG.1.

, 59 PEG. 8.

' 57 I I4 64 F IG. 9

RATE OF SPIN 0F BALLS ABOUT I 79 THE AXIS OF THE FUZE.

Feb. 7. 1956 s. w. BOOTH 2,733,659

DELAYED ARMING FUZE FOR A PROJECTILE Filed Aug. 5, 1949 2 Sheets-Sheet 2F 6 F. M.

66 w 67 as 14 {35 Elma/MM 4.1 m s SETH w. 00TH $5 United States PatentDELAYED G FUZE FOR A PROJECTILE Seth W. Booth, University Park, Md.Application August 5, 1949, Serial No. 108,833 12 Claims. (Cl. 102-79)(Granted under Title 35, U. S. Code (1952), see. 266) This inventionrelates to a fuze for a projectile, or the like, adapted to be firedfrom a gun and exploded upon impact with a target or in the vicinity ofa target, in which new and improved means are employed for preventingthe premature arming of the explosive or bursting charge until the shellhas traveled a safe distance beyond the muzzle of the gun. Morespecifically, the invention relates to a new and improved means formaintaining the fuze in a safe condition until the speed of rotation ofa plurality of inertial devices has approached the speed of rotation ofthe projectile.

In accordance with the present invention a plurality of balls arearranged between a pair of conical surfaces formed on a movable andstationary member respectively and disposed within the fuze of aprojectile whereby the speed of rotation of the balls as the projectileis fired from a gun is gradually increased until the force ofacceleration of the projectile has diminished to a value correspondingto the force of acceleration acting on the projectile at a safe distancefrom the gun after the projectile has been fired therefrom until apredetermined speed of rotative movement of the balls is obtained. 7

When this occurs the fuze is armed.

This invention provides new and improved means for preventing thepremature explosion of the shell or projectile in or within the vicinityof the gun as the gun is fired.

One of the objects of the present invention is the provision of a newand improved means for preventing the premature firing of an explosivecharge arranged within a projectile during'the transportation, handling,loading, and firing of the projectile from a gun.

Another of the objects is the provision of a new and improved means formaintaining a fuze in a safe condition as the projectile is fired from agun until the speed of rotation of a plurality of inertial ballsarranged be tween a pair of conical members having the axes thereof incoincidence with theaxis of the projectile has reached apredeterminedvalue.

Still another object is the provision of a fuze for a projectile havingnew and improved mechanical means for delaying the arming of the fuze asthe projectile travels along a trajectory and to render the electricalfiring mechanism effective when the centrifugal force produced by thespin of a plurality of balls has caused'movement of the arming mechanismof the projectile.

A further object is to provide a new and improvedfuze for an explosiveprojectile having means arranged therein for preventing arming andfiring thereof until the projectile is clear of the gun which iseconomical to manufacture, reliable in operation, and which possessesthe qualities of durability and safety during handling andtransportation.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

ice

Fig. 1 is a sectional view of the fuze of the present invention and aportion of a projectile or the like employed therewith, the fuze beingin an unarmed condition;

Fig. 2 is a sectional view similar to Fig. 1 and showing the fuze in anarmed condition;

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 1;

Fig. 4 is an enlarged fragmentary view of the delayed arming device withthe inertial elements thereof in an initial position;

Fig. 5 is a view similar to Fig. 4 and showing the position of theinertial element during movement of the armin g member toward an armedposition;

Fig. 6 is a diagrammatic view of the firing circuit therefor; v

Fig. 7 is a graph illustrating in diagrammatic form the delay in thearming of the fuze after the projectile has been fired from a gun;

Fig. 8 is a fragmentary view of the device according to an alternativeform thereof; and

Fig. 9 is a diagrammatic view of a firing system suitable for use withthe device of Fig. 8.

Referring now to the drawings for a more complete understanding of theinvention and more particularly to Fig. 1 thereof, there is shownthereon a fragmentary portion of a shell or projectile indicated by thereference character 10 and comprising a casing 11 having the usualexplosive or bursting charge 12 disposed therein, as is Well known tothose skilled in the art.

The fuze generally indicated by the reference character 13, comprises anose portion 14 secured to the shell casing 11 in any suitable manner,preferably by an external screw threaded nipple 18 having threadedengagement with the shell casing 11. The nipple 18 is provided with anenlarged well 19 having a booster charge 24 arranged therein andcomposed of any explosive suitable for the purpose such, for example, asthe type known in the trade as Tetyrl.

A reduced bore 25 is arranged within the nose 14 in communication with awell 19 and a lead-in explosive charge indicated by the referencecharacter 26 is disposed therein,in engagement with the booster charge24 to provide means for firing the booster charge when the fuze isfunctioned upon impact thereof with a target. The booster charge issealed within the recess by a disc 27 composed of any material suitablefor the purpose such, for example, as blotting paper or the like and asteel disc 31, the disc being clamped in position by a flange 32 formedon the magazine and crimped or rolled into clamping engagement with thedisc.

A delayed arming device generally indicated by the reference character33 is arranged within a recess 34 formed in the nose 14 with the axisthereof incoincidence with the spin axis of the projectile or missile.The arming device comprises a stationary member 35 and a movable member36, the members 35 and 36 having respectively formed thereon a pair ofcentrally disposed parallel surfaces 37 and 38 and a pair of outwardlyand downwardly inclined surfaces 39 and 41. Disposed between the members35 and 36 and in engagement with the surfaces 37-38 when the projectileis in an unarmed condition are a plurality of balls 42, the balls beingadapted to be moved radially by centrifugal force into engagement withthe inclined surfaces 39 and 41 thereby to move the member 36longitudinally sufficiently to arm the fuze during the flight of theprojectile toward a target.

As shown on Figs. 1 and 2 the member 36 has formed thereon a boss orextension 43, having secured thereto and movable therewith asubstantially L-shaped bracket or support generally indicated by thereference numeral 44 and comprising a short leg 45 and a long leg 46,the long leg being secured to the boss 43 in any suitable manner such,for example, as by screws or the like.

The nose 14 has formed therein a recess or guide-way 47 having a plunger48 releasably and slideably arranged therein. The plunger is normallylocked and urged to an armed position, Fig. 2, by a spring 49 when theplunger has been released, whereupon a sensitive detonator 51 is broughtinto registration with the lead-in charge. 26. It will be understood,however, that the plunger is locked in a safe or unarmed condition, Fig.l, by the usual centrifugally actuated detents (not shown), the detentsbeing adapted to be moved to a. release position in response tocentrifugal force whereupon the plunger 48 is moved to an armed positionby spring 49.

As shown on Figs. 1 and 2 nose 14. is provided with a bore or passageway52 comprising a vertical portion 53 and an inclined portion 54. Thevertical portion is in. communication with the recess 47 and hasdisposed therein a sensative detonator 55 in approximate spaced relationwith respect to the plunger 43. and adapted to fire. the detonator 51when the plunger is, in an armed position upon impact of the shell witha target. The inclined portion is in communication with a centrallydisposed bore 56 and has disposed therein a flash primer 57 adapted tobe fired by a firing pin 58 releaseably supported Within the bore 56 bya shear pin 59 as the pin is severed upon impact of the shell with atarget.

Disposed within the inclined portion 54 of the bore 52 is a detent 61,the detent being normally urged into a safe position by a spring 62,Fig. 2, thereby to prevent, communication between the bore 56 and theinclined portion 54 until the detent has been actuated to an armedposition in response to centrifugal force. When this occurs the detent61 will be moved from the safe position sufficiently to permitcommunication between the aforesaid bores and thus permitting a flashfrom primer 57 when fired by the firing pin 58 to contact and fire thedetonator 55.

As shown more clearly on Figs. 1 and 2 the member 36 is held againstrotative movement by a plurality of rods 50 secured thereto in anysuitable manner such, for example, as by having one end of each rod inthreaded engagement with member 36, the other ends thereof beingrespectively disposed and slideably arranged within a pluralityofrecesses formed in the nose 14. By this arrangement the member 36' ismoved longitudinally as the balls 42 are moved outwardly therebyassuring arming of the fuze. A spring 60 is arranged about each rod 50having one end in engagement with the. member 26, the other end thereofbeing in engagement with the nose 14 and thus. restraining the member 36until the force applied to the arming member by the. ballsv exceeds theforce applied thereto by the springs.

The detent 61 is provided with an annular locking groove 63 havingdisposed therein one end of a pawl or latch generally indicated by thereference character 64, the other end thereof being rotatably supportedon a, pivot pin 65. The; latch member 64 maintains the detent 61 lockedin a safe, position until actuated to a released position by the movablemember 36 as the member is moved longitudinally to an armed'positionduring the flight of the projectile. Furthermore, the movable member 36is main tained immovable and locked until the pawl 64 is moved out of.engagement with. the leg 45 formed on the L-shaped member 44, Fig. 2. Itwill be understood, however, that as. the spin. of the projectileincreases, rotative movement of the balls 42 disposed between the.members 35 and 36 is gradually accelerated and thereby the balls developsufficient centrifugal force to cause movement thereof outwardly intoforcible engagement with the inclined surfaces 39- 41, whereupon themovable member 36 is moved longitudinally within the. fuze in. response.to the radial movement.v of the balls. When this occurs. the leg 45moves. the latch, member 64 out. of engagement with the groove. 63formed in detent 61. and thus the. detent is unlocked. for movement to,the aforesaid. armed position Within the bore 54. The member 36 is alsoadapted to disengage the pawl 64 from the leg 45 upon movement thereof.

The operation of the inertial balls 42 in arming the fuze will best beunderstood by reference to Figs. 4 and 5, on which is shown the balls intheir initial position and before being moved outwardly into engagementwith the annular cam surfaces 39 and 41 of the members 35 and 36 and theposition of the balls during movement of the arming member 36 toward thearmed position thereof respectively. When the balls are in position asshown on Fig. 4 prior to movement of the arming member 36, the balls arein contact with the surfaces 38 and 39 at two diametrically disposedpoints thereof by reason of the action of the springs 60. The balls atthis time are not rotating at the same speed of rotation as the fuze byreason of the engagement of the balls between the polished surfaces 37and 38 of the members 35 and 36 and the smooth polished surfaces of theballs with which they are engaged. It will be understood, therefore,that during the initial travel of the fuze the balls are continuallyslipping between the surfaces 37 and 38 until the speed of rotation ofthe balls about the axis of the fuze has obtained sufficient proportionto cause movement of the member 36 from the initial unarmed positionthereof.

When this occurs the balls 42 are no longer engaged by the flat surfaces37 and 33 but are in rolling contact with the smooth annular inclinedsurfaces 39 and 41 at the points A and B, Fig. 5. The points ofapplication of force to the balls 42 are thus transferred from the pairof diametrically disposed points of contact of the balls with thesurfaces 37 and 38 to a pair of points A and B displaced at a distance Dfrom the axis of the balls whereby a moment is applied to each of theballs, causing the balls to spin about their axes as they roll alongcircular tracks on the. inclined surfaces 39 and 41. The additionalforce required to impart rotative movement to the balls about, theiraxes causes the balls to accelerate more slowly in their rotativemovement about the axis of the projectile than would otherwise be thecase and thus an additional delay is obtained in moving the armed member36 to the armed position. This condition is clearly made manifest onFig. 7' of the drawings in which the initial spin of the balls abouttheir axes is indicated at point 70 of the curve 77.

From the foregoing it will be, clearly apparent that the delay in armingthe. fuze is achieved by a plurality of spherical inertial membersfrictionally engaged between complementary cam surfacesv in which thecoefiicient of friction between the: spherical. surfaces and members issufliciently small to. cause a considerable degree of slippage betweenthe inertial members and the complementary surfaces. Movement of anarming member in response to the centrifugal force of these inertialspheres is, thus; delayed. until the spin missile has traveled a safedistance from the point of launching thereof. An additional andimportant feature of this delay feature resides in the spin. of theballs. about their axes upon fractional engagement of the balls withvthe annular inclined cam surfaces which causes the. rate of accelerationof the balls in their rotative movement about the axis of the spinprojectile to be retarded in proportion to the spin transmitted to theballs through their points of contact with the inclined surfacesaforesaid.

When the fuze has been armed, the detonator 51 is aligned with thelead-in charge 26 and also. brought in alignment with the primer 55, thedetent 61 having been moved. outwardly sufficiently to permit anuninterrupted passageway between primer 5755. Upon impact of the shellwith a target, the firing pin 58 is driven into firing engagement withthe primer 57 with sufiicient force to cause firing thereof, the. flashtherefrom being directed by way of. bores. 56,. 53', and 54 into firingengagement with primet 55; and thus initiating firing of the. detonator51', leadin charge 26, and booster charge 24' in successive order.

The arming of the fuze is delayed by the specific construction andarrangement of the delayed arming mechanism 33, particularly the balland cam arrangement thereof, for the reason when the projectile ormissile is fired or launched, as the case may be, and rotates about itsaxis the balls 42 gradually accelerate rotatively. This accelerationdevelops suflicient centrifugal force to cause the balls to moveoutwardly into engagement with the inclined surfaces 39 and 41, suchoutward movement of the balls along the inclined surfaces causing themovable member 36 to be moved longitudinally with respect to thestationary member 35 in predetermined time delayed relation with respectto the initial rotation of the missile as the missile is fired.

It will be understood, however, that when the member 36 has been movedlongitudinally as heretofore described means may be employed therewith,if desired, for arming the fuze electrically.

As shown on Figs. 1 and 2 means are employed to arm the fuze by movementof the member 36 and to fire the fuze electrically, the means comprisinga pair of normally closed contacts 66--67 and a pair of normally opencontacts 6869, the contacts 66 and 69 being electrically connectedtogether and secured to the movable member 36. When the fuze is in anarmed condition, a firing circuit is established from the firingmechanism 71, Fig. 6, of any well known type suitable for the purpose tothe electroresponsive detonator 72 by way of conductor 73, contacts 68and 69, and conductor 74 to one terminal of the detonator 72, the otherterminal of the detonator being connected to the firing mechanism byconductor 75. The fuze is maintained in a safe condition during handlingand transportation by the detent 61 and latch 64 and also by theforegoing circuit arrangement whereby the electroresponsive detonator 72is normally short circuited by contacts 6667 as clearly shown on Fig. 6.

The firing mechanism 71 may be of any type suitable for the purpose,such for example, as a radio controlled firing mechanism or the voltagegenerating device disclosed and claimed in the co-pending application ofHarold J. 'Plumley, for a Magnetic Inertial Controlled Fuze, Serial No.535,799 filed May 16, 1944.

By the foregoing arrangement it will be understood that a firing circuitwill not be established from the firing mechanism to theelectroresponsive detonator until the movable member 36 has been movedto an armed position in the aforesaid manner, thereby moving the member36 sufiiciently to engage contacts 6869 and to disengage contacts 6667.It will be understood, however, that movement of the detent 61, Fig. 1,will not occur until the member 36 has moved a sufficient distance todisengage the latch member 64 therefrom and thus complete arming of thefuze will not occur until the shell has cleared the muzzle of the gunand traveled a predetermined distance therebeyond sufiicient to causethe balls within the members 35 and 36 to spin at a rate at which themember 36 is moved thereby to an armed position.

The lag in the rateof spin of the balls with respect to the spin of theprojectile and the delay in arming caused thereby will best beunderstood by reference to Fig. 7 on which it is shown by the curve 76the rate of spinof the projectile as the projectile is fired from thegun and travels along a trajectory. The rate of spin of the balls aboutthe axis of the projectile within the members 35 and 36 is shown by thecurve 77. The angular acceleration'of the balls from a state of rest tothe rate of spin corre sponding to the spin of the projectile requires amuch longer period of time to achieve than the time required for theshell to reach a state of maximum rate of spin by reason of slippage ofthe balls between the elements 35 and 36 during the initial portion ofthe flight of the projectile. The dashed line 78 is employed to indicatethe rate of spin of the balls required to generate centrifugal forcesufiicient to move the balls outwardly and thus actuate the member 36 tothe armed position. The intersection of the dashed line 78 with thecurve 77 at point '6 79 occurs at a time T sufiicient for the projectileto be well clear of the gun before the member 36 is extendedsufiiciently for contacts 6667 to be disengaged and contacts 6869 to bebrought into mutual engagement and thereby close the firing circuit fromthe firing mechanism to the detonator 72.

From the foregoing it will be apparent that the firing mechanism and thecircuit arrangement therefor is particularly well adapted to functionthe fuze electrically when the projectile strikes the target and thefiring pin 58 is adapted to function the fuze mechanically when theprojectile strikes the target a head-on blow in which event the fuze isfired by the firing pin.

As shown on Fig. 8 a cup-shaped member 81 is employed on the boss 43 inplace of the L-shaped bracket 44 for releasing the latch member 64 asthe member 36 is moved longitudinally thereby to arm the fuze asheretoi'ore described. The member 36 in accordance with this form of theinvention is restrained by a pair of springs 82, one end of each springbeing secured to the nose 14 as at 83, the other end thereof being inengagement with the member 36 as at 84. Secured to the boss 43 is acontact ring 85 normally in engagement with a contact spring 86 and inspaced relation with a contact spring 87, the contact. springs 86-87being insulated from each other as at 88 and secured to the nose in anysuitable manner whereby the contactring 85 is disengaged from contact 86and brought into engagement with contact 87 as the member 36 moves intothe armed position.

The fuze is maintained in a safe condition and premature firing of thedetonator 72 will not occur for the reason that the detonator isnormally short circuited by contacts 86-85, Fig. 9.

When the fuze is in an armed condition, the short circuit is removedfrom the detonator and a firing circuit is established from the firingmechanism 71 by way of conductor 89, spring contact 87, ring contact 85and thence to grounded terminal of detonator 72, the other terminal ofthe detonator being connected to the firing mechanism by conductor 91.

By employing the arrangement'shown on Figs. 8 and 9 the arming member 36is adapted to move both longitudinally and rotatively with respect tothe shell while the shell is in flight, in contradistinction 'to thearrangement of Fig. 1 in which the arming member 36 is restrained fromrotative movement with respect to the shell.

In operation as the shell is fired from a'gun sudden rotative movementis imparted to the member 35 secured integrally thereto and the inertialballs 42 rotate about the axis of spin of the shell with increasingrapidity, the rate of rotative movement of the balls about the spin axisof the projectile lagging the spin of the projectile. The member 36 iscaused to spin about the aforesaid axis of rotation of the shell with agradually increasing rotative speed'by reason of the moment appliedthereto by the springs 82, contact spring 86, arm 64 and the frictionbetween the element 36 and the support therefor. By reason of thisconstruction a greater delay in the time required for the inertial ballsto attain a rate of spin sufiicient to actuate the member 36 to an armedposition may be obtained than with the arrangement of Fig. 1. It will beunderstood, however, that either of the devices of Fig. l or Fig. 8 maybe employed to achieve the desired result.

Whereas the invention in accordance with a preferred embodiment thereofhas, been described with particular reference to arming a projectileelectrically by actuating electrical contacts as the member 36 is movedlongitudinally, it is not so limited as, if desired, the member 36 maybe employed to cause motion in a mechanical arming system sufiicient tomove the components thereof into armed position as the member 36 ismoved by the balls in response to the centrifugal force of the balls asthe projectile rotates and the speed of rotation of the balls reaches apredetermined value during the flight of 7 the missile without departingfrom the spirit or scope of the invention. Furthermore, the member 36may he provided with a restraining spring or the like for additionallyretarding longitudinal movement of the member if desired.

Whereas the invention has been described in detail with respect to aprojectile, it will be understood, that it may be advantageouslyemployed, if desired, with a spin rocket or other missile which rotatesduring travel thereof toward a target.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than specifically described.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

I. An arming device for a fuze comprising a rotatable casing, an armingmember slideably arranged Within the casing, means including a pluralityof inertial balls in frictional engagement with said member foractuating the member to an armed position as the speed of rotation ofthe balls about the axis of rotation of the casing approaches the speedof rotation of the member, and means including a bell-crank leverpivotally mounted on said casing, and operated by said member, formaintaining the fuze in a safe condition until the member is actuated tosaid armed position.

2. An arming device for a fuze comprising a rotatable casing, an armingmember slideably arranged within said casing for movement along the axisof rotation thereof, means including a plurality of inertial balls infrictional engagement with said member for actuating the member to anarmed position in time delayed relation with respect to the initialrotation of the casing as the speed of rotation of the balls approachesthe speed of rotation of the casing, a normally locked detent slid ablyarranged within said casing for maintaining the device in a safecondition until the detent is released and moved in response to thespeed of rotation of the casing,

and a bell-crank lever in locking engagement with said detent andpivotally mounted on said casing for releasing the detent for slidingmovement as the member is actuated to said armed position.

3. In an impact fuze for a spin missile, a casing, an explosive chargearranged within said casing, a movable member arranged within said fuzein coincidence with the axis of spin of the missile for arming the fuzewhen the member has been moved longitudinally, means including aplurality of inertial balls in frictional engagement with the member formoving the member longitudinally to an armed position in predeterminedtime delayed relation with respect to the initial spin of the missilewhen the balls are moved outwardly in response to centrifugal force asthe spin of the balls approaches the spin of the member, means includinga bell-crank lever pivotally mounted on said casing and actuated by themovement of the member for arming the fuze when the member has beenmoved longitudinally a predetermined amount, and means responsive toimpact of the missile with a target for firing said explosive charge.

4. In an impact fuze for a spin missile, a casing, an explosive chargearranged within said casing, a movable member arranged within the fuzeand constructed and arranged to be moved longitudinally in predeterminedtime delayed relation with respect to the initial spin of the missile,means including a plurality of balls in frictional engagement with themember and disposed about the axis of rotationthereof and responsive tomovement of said bails caused by centrifugal force as the spin of theballs approaches the spin of the missile for moving the member apredetermined amount, means including. a bell-crank lever pivotallymounted on said casing in engagement with the member and operatedthereby as the member is moved said predetermined amount for arming thefuze, and means responsive to impact of the missile with a target forfiring said explosive charge;

5. In an impact fuze for a spin missile, a casing, an explosive chargearranged within said casing, a movable member arranged within said fuzeand having a first annular inclined surface arranged thereon, a memberarranged within the fuze and having a second annular inclined surfacearranged thereon in opposition and spaced relation with respect to saidfirst inclined surface, a plurality of balls disposed between saidmembers and within said inclined surfaces for moving the movable memberlongitudinally as the balls are moved outwardly along said inclinedsurfaces in response to centrifugal force as the spin of the ballsapproaches the spin of the missile, means including a bell-crank leverpivotally mounted on said casing and responsive to the movement of themovable member for arming the fuze when the member has been movedlongitudinally a predetermined amount, and means responsive to impact ofthe missile with a target for firing said explosive charge.

6. In a fuze for a spin missile, a casing, an explosive charge arrangedwithin said casing, a movable member arranged within said fuze, meansincluding a plurality of balls responsive to centrifugal force as thespin of the balls approaches the spin of the missile for moving themember longitudinally within the fuze, a normally open firing circuitarranged within the fuze, means responsive to movement of said memberfor closing the firing circuit as the member is moved by said balls,means including a bell-crank lever pivotally mounted on said casing andoperated by said member for maintaining the fuze in a safe conditionuntil said member has been moved by the balls and said firing circuithas been closed, a firing device ar ranged within said circuit forgenerating an electrical firing impulse as the missile moves intoproximate relation with respect to a target, and an electroresponsivedetonator included within the firing circuit and adapted to be fired inresponse to said electrical impulse.

7. In a fuze for a spin missile, a casing, an explosive charge arrangedwithin said casing, a movable member arranged within said fuze, meansincluding a plurality of balls in engagement with said movable memberand responsive to centrifugal force as the spin of the balls approachesthe spin of the missile for moving. the member longitudinally within thefuze, a normally open firing circuit arranged within the fuze, meansresponsive to movement of said member for closing the firing circuit asthe member operates, means including a bell-crank lever pivotallymounted on said casing and operated by said member for maintaining thefuze in a safe condition until the member has been moved longitudinallya predetermined amount and said firing circuit has been closed, a firingdevice arranged within said circuit for generating an electrical firingimpulse as the missile moves into close proximate relation with respectto a target, an electroresponsive detonator included within the firingcircuit and adapted to be fired in response to said electrical impulse,and means on the member for short circuiting the detonator until themember has been moved longitudinally.

8. An arming device for a spin projectile comprising a movable armingelement, means for normally maintaining the arming element in an initialunarmed postion, means including a pluralityof balls for moving thearming element to an armed position as the speed of rotation of theballs approaches the speed of rotation of the projectile, and meansincluding a bell-crank lever pivotally mounted on said. device andoperated by said element. for arming said device as" the element ismoved to said armed position.

9; An arming device for a spinprojectile comprising arranged in spacedrelation with respect to said first named member, means for normallymaintaining the arming member in an initial unarmed position, meansincluding a plurality of balls disposed between said members for movingthe arming member to an armed position as the speed of rotation of theballs about the axis of the projectile approaches the speed of rotationof the projectile, and means including a bell-crank lever pivotallymounted on said device and operated by said member for arming the deviceas the member is moved to said armed position.

10. An arming device for a spin projectile comprising a movable armingelement, means for normally maintaining the arming element in an initialunarmed position, a pair of inclined annular cam surfaces arrangedwithin the arming device, a plurality of balls arranged between andnormally out of engagement with said cam surfaces for moving the armingelement longitudinally to an armed position as the balls are movedoutwardly into engagement with said cam surfaces in response tocentrifugal force, and means including a bell-crank lever pivotallymounted on said device and operated by said element for arming thedevice as the element is moved to said armed position.

11. An arming device for a spin projectile comprising a movable armingelement, an inclined cam surface on said arming element, means fornormally maintaining the arming element in an initial unarmed position,a stationary element in the arming device, a second inclined cam surfaceon said stationary element and spaced from said first named inclined camsurface, a plurality of balls disposed between said inclined surfacesand normally out of engagement therewith for moving the arming elementto an armed position as the balls are moved into engagement with saidcam surfaces in response to centrifugal force, a normally locked detentfor maintaining the device in a safe condition until the element hasbeen moved to said armed position, and a bell-crank lever pivotallymounted on said device in locking engagement with said 10 detent forreleasing the detent as the element is moved to said armed position.

12. An arming device for a spin projectile comprising a movable armingelement, means for supporting said element within the projectile forlongitudinal and rotative movement with respect to the spin axisthereof, a complementary element secured within the arming device, apair of frusto-conic cam surfaces respectively disposed on said elementsin mutually matching spaced relation, a plurality of inertial ballsdisposed within said cam surfaces, means for yieldably urging saidmovable element into engagement with the balls whereby the balls areinitially maintained within a predetermined circumferential area betweensaid elements in contact with said surfaces when the movable armingelement is in an unarmed position, said balls having sufiicient mass tomove the arming element longitudinally to an armed position in timedelayed relation with respect to the firing of the spin projectile froma gun when the speed ratios of rotative movement of the balls and thearming element with respect to the spin of the projectile has reached apredetermined value, a normally locked detent slidably arranged withinsaid device for maintaining the device in a safe condition until thedetent is released and moved a predetermined amount in response to thespin of said projectile, and a bell-crank lever in locking engagementwith said detent and pivotally mounted on said device for releasing thedetent as the element is moved to said armed position.

References Cited in the file of this patent UNITED STATES PATENTS2,118,062 Woodberry May 24, 1938 2,167,197 Brandt July 25, 1939 FOREIGNPATENTS 125,649, Great Britain May 1, 1919 130,084 Great Britain July31, 1919 573,621 Great Britain Nov. 29, 1945

